Bow Thrusters and battery charging etc.

[Biggles]

I have installed my bow thruster, and the batteries to run it and I have laid in some heavy charging wires back to the engine, but not a heavy as the bow thruster to battery supply cables.

 

My question is relating to the charging cables when the bow thruster is deployed. These wires will remain in circuit during BT operation. Am I right in thinking the BT to battery cables will be the first ones to deploy so no appreciable current will be drawn down the charge wires.

 

Should I isolate these on BW deployment or not worry about it?

 

Biggles

[WotEver]

Personally, I wouldn't worry about it. You'll have such a volt drop down the long lines even if they are fat that I'd be very surprised if you pull anything significant out of the domestics. This is one of the arguments for not using particularly heavy lines down the boat; the BT batt will still get charged down smaller ones, and you don't need to worry about dragging down the domestics.

 

How are you fusing these long lines?

 

Tony

[Timleech]

I have installed my bow thruster, and the batteries to run it and I have laid in some heavy charging wires back to the engine, but not a heavy as the bow thruster to battery supply cables.

 

My question is relating to the charging cables when the bow thruster is deployed. These wires will remain in circuit during BT operation. Am I right in thinking the BT to battery cables will be the first ones to deploy so no appreciable current will be drawn down the charge wires.

 

Should I isolate these on BW deployment or not worry about it?

 

Biggles

 

You don't want BW staff to see how you've done it?

 

The experts will be along in a bit, but I should think the main thing to do is make sure that these cables are correctly fused (edit - at both ends) as protection against overheating, in case the BT does try to run from the main batteries.

 

Tim

Edited August 25, 2011 by Timleech

[WotEver]

It would of course be very simple to wire a contactor (big relay) in line with one of the cables so that it disconnects that feed when the BT is powered.

[blackrose]

My long BT cables continue to charge the batteries (or at least they remain in circuit) when my BT is used. They would even continue to charge if the BT batteries are isolated and engine run because the isolator is between the batteries and the BT motor.

 

Personally, I wouldn't worry about it. You'll have such a volt drop down the long lines even if they are fat that I'd be very surprised if you pull anything significant out of the domestics. This is one of the arguments for not using particularly heavy lines down the boat; the BT batt will still get charged down smaller ones, and you don't need to worry about dragging down the domestics.

 

How are you fusing these long lines?

 

Tony

 

Does this assume that the arrangement is a split charge between domestic and BT batteries? My system splits the charge between start and BT batteries - both utilising the start alternator. I might be wrong but I don't think any excess charge could be drawn from the start battery by the BT motor because the splitting is done by this device. http://www.bepmarine.com/home-mainmenu-8/product-269/125-amp-voltage-sensitive-relay-vsr-

 

Since most new boats have twin alternators these days, why isn't a start/BT split charge system more common? Because the smaller start battery is easier and quicker to top up, it seems to make more sense than splitting the charge between domestics and BT.

Edited August 25, 2011 by blackrose

[Gibbo]

It can be a bit of pain this one. You have to weigh up lots of compromises.

 

First thought is usually to put huge cables in to counter the volt drop. But when you think about it properly you realise that you only get volt drop during really heavy charging. As the BT batteries come up to full charge they draw less current so the volt drop reduces and they will indeed get properly charged. During normal cruising, unless you use your BT like a dick this is usualy plenty sufficient.

 

If you're someone who uses the BT loads then you can run into problems of never properly charging the batteries up because you're taking it out as fast as you're putting it in because the charge rate is limited by the small cable size. Then you have to revert to huge cables.

 

Assuming you realise you can get away with smaller cables you then have to consider fusing. They (as Tim pointed out) need to be fused at both ends. What size fuses? They have to protect the cable with a short to hull at the far end. So you have to work out the cable resistance and what current it will draw under worst case scenario. Then fuse for that.

 

But then, sometimes, some people will say, depending upon the size of the cable, you might find that even a direct short won't draw enough current to harm the cable so a fuse isn't needed. Of course it is! The short might be at the closest end not the far end.

 

When you do this properly, no matter what combination of cable size, boat length etc, you will find that the only correct way of doing it involves isolating the split charge feed when the BT is operated otherwise it will pop the fuses if the BT battery is low on charge.

 

Any installation that doesn't pop the fuses, has the wrong size fuses. It's that simple.

 

The reason for this ridiculous complication in comparison to a normal battery feed is quite simply that it has a power feed at both ends. You should see how complex this problem becomes on the national grid which has hundreds of power feeds spread all over it.

 

Good innit

[Biggles]

I will fuse it both ends with a 100amp fuse unless the advice is different. I have run 25mm Most of the length of the boat so about 18 m

 

This is a twin alternator system the alt that charges the start battery also charges the BT batteries. The other one is dedicated to the domestics.

[Gibbo]

I will fuse it both ends with a 100amp fuse unless the advice is different. I have run 25mm Most of the length of the boat so about 18 m

 

But....

 

When you do this properly, no matter what combination of cable size, boat length etc, you will find that the only correct way of doing it involves isolating the split charge feed when the BT is operated otherwise it will pop the fuses if the BT battery is low on charge.

 

Any installation that doesn't pop the fuses, has the wrong size fuses. It's that simple.

[blackrose]

When you do this properly, no matter what combination of cable size, boat length etc, you will find that the only correct way of doing it involves isolating the split charge feed when the BT is operated otherwise it will pop the fuses if the BT battery is low on charge.

 

Any installation that doesn't pop the fuses, has the wrong size fuses. It's that simple.

 

The reason for this ridiculous complication in comparison to a normal battery feed is quite simply that it has a power feed at both ends. You should see how complex this problem becomes on the national grid which has hundreds of power feeds spread all over it.

 

Good innit

 

So then, what is the best practical solution to this problem?

[Biggles]

So then, what is the best practical solution to this problem?

 

Yes, good question.

 

Seems that most work well without having to isolate the charge lines. I will try it with the fuses first. If it pops the fuses then a connector will be deployed. I have already found the wiring that will facilitate this at the BT control end.

 

Or should I ?

[smileypete]

So then, what is the best practical solution to this problem?

Bigger fuse

 

cheers,

Pete.

[Biggles]

Bigger fuse

 

cheers,

Pete.

 

Likey

[blackrose]

Any installation that doesn't pop the fuses, has the wrong size fuses. It's that simple.

[smileypete]

Well, you wanted something practical?

 

How about an alternator with external rectifier?

 

Or feed the BT from batts at the back via aluminium bus bars?

 

20mm square bar is the same as 240mm² copper...

 

cheers,

Pete.

Edited August 25, 2011 by smileypete

[Gibbo]

So then, what is the best practical solution to this problem?

 

Disconnect the split charge whilst the BT is beiing used. A feed from the BT control is used to interrupt the feed with a big relay.

 

Bigger fuse

 

You say that in jest. It is indeed what usually gets done.

Edited August 25, 2011 by Gibbo

[dove]

So then, what is the best practical solution to this problem?

 

Don't fit a Bow thruster...save energy and save the canal banks. Use your foot, you're not docking a car ferry.

 

Andrew

[blackrose]

Don't fit a Bow thruster...save energy and save the canal banks. Use your foot, you're not docking a car ferry.

 

Andrew

 

 

Didn't you read the OP? It's already been fitted. He just wanted to know the best way to set up the electrics.

 

Save the canal banks? How powerful do you think a bow thruster that's fitted to the average canal boat is? People do far more damage with their props.

 

As for using your foot - never put your foot between a moving boat that's coming in and the bank! Anyway, being single-handed I'd need very long legs to reach the bow from the helm with my foot.

Edited August 26, 2011 by blackrose

[Tam & Di]

So then, what is the best practical solution to this problem?

 

 

Tear it all out and fit a hydraulic one. Hydraulics can be used virtually non-stop if necessary, as with a JCB. I have to concede that bow thrusters are useful when you are reversing some long distance, but you need something powerful that you can rely on, not a kitchen vent-axia fan.

[blackrose]

Tear it all out and fit a hydraulic one. Hydraulics can be used virtually non-stop if necessary, as with a JCB. I have to concede that bow thrusters are useful when you are reversing some long distance, but you need something powerful that you can rely on, not a kitchen vent-axia fan.

 

Nonsense! I've used my electric BT for 6 years without a problem and I've seen just as many problems with hydraulic BTs as electric units. Why would anyone want to use a BT non-stop? Since we're not supposed to be overusing them, electric BTs are fine. I've used mine to reverse long distances, but only needed to use the BT in short bursts.

 

Also a BT doesn't need to be powerful to shift the bow of a canal boat, it just needs to be properly installed. Think about how little pressure is needed to move the bow of a moored canal boat with your leg when you're standing on the bank. My boat weighs 32 tonnes but it doesn't take much to move the bow.

Edited August 26, 2011 by blackrose

[Ark Right]

I have installed my bow thruster, and the batteries to run it and I have laid in some heavy charging wires back to the engine, but not a heavy as the bow thruster to battery supply cables.

 

My question is relating to the charging cables when the bow thruster is deployed. These wires will remain in circuit during BT operation. Am I right in thinking the BT to battery cables will be the first ones to deploy so no appreciable current will be drawn down the charge wires.

 

Should I isolate these on BW deployment or not worry about it?

 

Biggles

This method works, from a fag packet drawing from Mick Sivewright (Vetus Kings Lock Chandlery)

8.5mm charge cables from primary alternator via a 70amp relay energised from the ignition switch, 50 Amp fuses at each ends of the charge cables.

Out of 10 installs only one has had a charge fuse blow, no big deal it just flagged up to him he was overdoing the use of the thruster.

Cheers

A

[Tam & Di]

I've used mine to reverse long distances, but only needed to use the BT in short bursts.

 

You're probably right. We operated a large range of craft in the UK from freight narrowboats, passengerboats, tugs and barges to small coasters. None of these had a bow thruster and I never thought they would be useful. With our 24m motorbarge for use in continental waters I did fit one. I find I mostly use it as an instructor's override when a trainee tries to ram a lockside, but do find it useful when reversing a couple of kilometers to a winding hole.

 

Unfortunately we see a hell of a lot of inexperienced barge owners here who seem to rely on their bow/stern thrusters rather than learning to use a wheel (tiller, to those in the UK!). Their electric ones give them a false sense of security. Obviously it would be better to learn to steer properly, but they've paid their money to the builder so they do not have to do that.

 

I'm still unconvinced of the necessity on UK canals, but that is another argument. It probably relates to the poor handling characteristics of modern craft as much as to lack of skill of a steerer.

Edited August 26, 2011 by Tam & Di

[Ark Right]

Tear it all out and fit a hydraulic one. Hydraulics can be used virtually non-stop if necessary, as with a JCB. I have to concede that bow thrusters are useful when you are reversing some long distance, but you need something powerful that you can rely on, not a kitchen vent-axia fan.

 

Hydraulic bow thrusters can be used all day long, quite right. The flaw in the use of hydraulics for this operation is that in normal conditions a thruster is used for low speed manoeuvring, requiring low engine revs. This usually results in poor performance from the thruster as the engine revs are not high enough for the hydraulic pump to be delivering optimum power.

Hydraulic systems which power both propulsion and thruster overcome this to a point but that is not what is being discussed in this thread.

Cheers

A

[Tam & Di]

Hydraulic bow thrusters can be used all day long, quite right. The flaw in the use of hydraulics for this operation is that in normal conditions a thruster is used for low speed manoeuvring, requiring low engine revs. This usually results in poor performance from the thruster as the engine revs are not high enough for the hydraulic pump to be delivering optimum power.

Hydraulic systems which power both propulsion and thruster overcome this to a point but that is not what is being discussed in this thread.

Cheers

A

 

Since when did CWF threads stay on topic?

With any Morse style control you can always disengage the thrust and rev the engine to give additional power to the bow thruster. With a system designed to give full power to the hydraulics throughout the revs of the main engine you can overcome this anyway, other than if you have a slow revving old engine such as our Gardner.

 

OK, back to a discussion of electrics.

[Biggles]

I think form this I have decided to use the 2 fuse system. If this proves unreliable then I will introduce a connected to the line operated when the BT is switched on.

[Tam & Di]

Anyway, being single-handed I'd need very long legs to reach the bow from the helm with my foot.

 

My analogy when people are trying to use their bow thruster instead of their wheel/tiller is that it is simply an alternative to having someone on the fore end with a long shaft - something you do only rarely. If you are working one-handed it is obviously more useful, but my comment still applies to those who see a bow thruster as an alternative to learning the skills of steering a boat.